Can Labour pull it off, and what would be the price? If Gordon Brown, or his successor, were able to assemble an extraordinary multicolour informal coalition of Labour, Liberal Democrats, four SDLP MPs, one Northern Ireland Alliance member, six Scottish nationalists, four Welsh nationalists and one Green, this rag-tag group would command more than the 324 votes necessary to form a majority. This is all on the shaky assumption that Labour ends up with 261 seats and the Liberal Democrats hold 54.

On this basis, it would even be possible to form a coalition without one or other of the nationalist parties.

But the SNP says they will not join a coalition, while the Welsh nationalists want £300m extra funding for Wales. This pork barrel politics will not enthuse many English voters.

So this prospective coalition does not quite match Brown's promise that he will only govern if he can form a stable government

Brown also knows that he has to think hard about the state of public opinion. A senior Brown aide rang me almost at 10 o clock last night, as polls closed, to warn me that he thought Britain was heading for a hung parliament, and if the Tories got anywhere between 300 and 320 seats, it might just be possible to form a coalition with the Liberal Democrats.

But the aide warned Labour would talk a long game, knowing it would come under sustained pressure from the Tories and the rightwing press that Brown hand the keys over to Number 10 immediately. The aide was spot on, even informing me some of the unusual seats he expected Labour to hold.

David Dimbleby, seeking to express the potential outrage of Middle England, just now asked out loud on the BBC whether Brown would bear in mind what is fair - that the Conservatives have won many more seats and 2m more popular votes than Labour.

Would it be cricket for Brown to try to stay on, Dimbleby asked. The difficulty with this argument is that two teams are not playing cricket, and once you put Labour and the Liberal Democrat seats together, the yellow-red alliance has more seats than the Tories and far more of the popular vote.

Under the British constitution, currently in the hands of the cabinet secretary, Sir Gus O'Donnell, it is up to the sitting prime minister to see if he can put together a Commons majority for his Queen's speech.

Lord Mandelson has even gone so far as to suggest that it may be possible for Gordon Brown to stand down as leader, allowing someone else to come forward to see if he can secure a majority. O'Donnell will be desperate to avoid the Queen becoming too embroiled, and also knows that the very worst option is deadlock, followed by an immeduate second election.

Labour is now pleading with the Liberal Democrats to consider whether they are going to abandon their one and only chance to introduce electoral reform, or instead spurn Labour, recognising that a coalition of losers is just wrong.

Clegg could for instance settle with tempering some of the Conservative plans to rein back Tory cuts this year. He may also know that some of his party might rebel, and even cross the floor, if he insists on trying to form an alliance with Labour, led by Brown or a fresh faced Miliband.

My understanding is that Clegg, tired and despondent, is very wary of forming a coalition with Labour, but he has to think hard about how his party is to grow after the massive disappointment of last night.

On the basis of this vote, a breakthrough is unachievable under first-past-the-post. His options are not good.